Reduction Of Hydrogen Production Research Articles

Phase transition Ni-Co-Ca-O bifunctional catalysts for high and stable hydrogen production from sorption enhanced steam methane reforming

Sorption enhanced steam methane reforming (SESMR) is an effective method to improve the efficiency of hydrogen production from methane reforming while fixing CO2 to reduce carbon emissions. However, the deactivation of adsorbents during high temperature recycling limits the utilization of SESMR. In this paper, by combining the phase transition process of Ca-Co-O species and Ni-Co alloy, we prepared a series of Ni-Co-Ca-O bifunctional catalysts for SESMR hydrogen production. The 1Ni4.5Co4.5CaO catalyst exhibited high catalytic activity in the SESMR reaction with hydrogen concentration exceeding 99.6 % and complete methane conversion. The catalyst also showed high stability in 50 cycle experiments with no significant reduction in hydrogen production and CO2 uptake performance. The Ni-Co-Ca-O bifunctional catalysts consisted of NiO and Co-Ca-O species, by analyzing the fresh and reacted catalysts, the mechanism of the catalyst with high catalytic activity and stability was revealed. Firstly, the catalyst formed Ni-Co alloy and CaO adsorbent by a reduction reaction, and then the SESMR hydrogen production reaction was carried out. After the complete conversion of CaO to CaCO3, the catalyst was re-formed into NiO and Co-Ca-O species by introducing O2 in the regeneration reaction to carry out a new cycle of reduction → hydrogen production. The synergistic interaction between the Ni-Co alloy enhanced the methane reforming and water gas shift reaction, leading to an increase in hydrogen production and methane conversion. The phase transition of Co from Co-Ca-O species to Ni-Co alloy and back to Co-Ca-O species inhibited the sintering of CaO, which significantly enhanced the cyclic stability of the catalyst. The results of this study are expected to provide a new pathway for the design of SESMR bifunctional catalysts.

An integrated alkali metal thermoelectric converter with sodium hydroxide thermoelectric water splitter and organic Rankine cycle for efficient power and hydrogen production

This study proposes the integration of the NaOH thermochemical water splitting cycle with both an alkali metal thermoelectric converter and an organic Rankine cycle. The objective of the proposed model is to enhance the overall efficiency by utilizing the waste heat generated by the NaOH thermochemical water splitting process and redirecting the heat from the alkali metal thermoelectric converter using bypass when hydrogen demand is low.Performance parameters such as system efficiency, system power, hydrogen production, AMTEC power production, and ORC power production were examined in the study. The results indicated an increase in power and hydrogen production with higher hot-end temperatures, along with an overall reduction in system efficiency for low values of load resistance. The system achieved a maximum efficiency of 53.37%.The system efficiency reached its peak at an AMTEC hot end temperature of 1173 °C, achieving 53.37 % efficiency at an RL value of 1.01 O. When the system operates at its maximum AMTEC power production, the AMTEC modules supply 12.81 kW, while the ORC generates 5.57 kW, and the hydrogen compressor consumes 0.13 kW. The total electrical power generation is 18.38 kW. The findings also indicate that the utilization of the bypass led to a reduction in hydrogen production while increasing the power output of the organic Rankine cycle.

Synthesis of visible light-sensitive photocatalysts for hydrogen production

Photocatalysis is a promising way to produce green hydrogen from water under sunlight. However, it is still challenging to develop an efficient photocatalyst for hydrogen production that works under sunlight with high efficiency. In this study, sincere efforts have been made to develop a photocatalyst with enhanced light absorption within the visible spectrum and improved separation of photogenerated electron-hole (e-/h+) pairs. Phosphorus and Nickel codoped TiO2 (PNT) photocatalysts were synthesized through the sol–gel method by varying the amount of phosphoric acid, nickel nitrate, and calcination temperature. Photoluminescence and UV–Vis spectroscopy confirm that codoping enhances the separation of photogenerated e-/h+ pairs as well as improves visible light absorption. Codoped TiO2 had a higher specific surface area and higher pore volume than doped and pure TiO2. 1.5 wt% P and 3.0 wt% of Ni codoped TiO2 calcined at 400 °C (3.0 PNT 400 °C) shows the highest H2 production from water (266.471 μmolg-1h−1) and simulated seawater (148.536 μmolg-1h−1) under solar simulator bulbs in the presence of Ethylene Glycol (10 vol%). This photocatalyst exhibits good stability, with a slight reduction in hydrogen production of 9.15 % in water and 14.8 % in simulated seawater after four cycles.

The multi-scenario projection of cost reduction in hydrogen production by proton exchange membrane (PEM) water electrolysis in the near future (2020–2060) of China

The production and utilization of green hydrogen is of utmost importance to achieve the dual carbon national strategy of China, i.e., carbon peaking in 2030 and carbon neutrality in 2060. The proton exchange membrane water electrolysis (PEMWE), with the advantage of the fast dynamic operation adapting to the non-uniformity and intermittency of renewable energy, is capable of producing hydrogen with higher purity. To calculate hydrogen production costs from 2020 to 2040, we used the bottom-up method to determine the capital cost of PEM electrolyzers, which is brought into the H2A model along with electricity price predicted for China. In 2040–2060, the learning curve was used to predict the decline of the capital cost of the electrolyzer. We analyzed two scenarios during this period, considering whether the operational performance of the electrolyzer such as voltage and current density is improved. The calculated cost of hydrogen production will reduce from 7.26 $/kg to 2.60 $/kg mainly because of the capital cost reduction of the electrolyzer system from 4450 $/kW to 812 $/kW and the decline of the electricity cost. The capital cost and electricity cost account for 47.6% and 34.7% of the current total cost, respectively, while the electricity cost is projected to be the dominant and will account for 56.4% of the total cost in the scenario of 2040–2060. The cost price of 2.60 $/kg will show an advantage when the carbon tax of 78.82 $/t CO2 eq. for coal gasification and 107.48 $/t CO2 eq. for steam-methane reforming are imposed.

Biohydrogen potential assessment of Opuntia spp.: Effect of inoculum-to-substrate ratio and residual biomass evaluation

Opuntia spp. are considered bioenergy crops for contributing against global warming while avoiding water scarcity and declining fertile land problems in their cultivation. Unfortunately, these have been scarcely researched. This work targets to evaluate the biohydrogen potential of three Opuntia varieties (Opuntia ficus-indica var. Milpa Alta, OfiM; O. ficus-indica var. Copena, OfiC; and O. engelmannii, Oeng). Hydrogen production evaluated at three inoculum-to-substrate ratios (ISR) for OfiM and OfiC, showed that the ISR decrease was inversely proportional to the maximum hydrogen cumulative production and the highest hydrogen production rate. Afterwards, hydrogen production using methanol extracted residual biomass was demonstrated feasible but resulted in a reduction in hydrogen production. The best results attained were 438 mL H2 (41 mL H2/g VS) for OfiC at ISR 0.2 The use of Opuntia species for hydrogen production should be further explored to increase its competitive potential and the possibilities of new paths on bioprocesses integration.

Facile synthesis of black N-TiO2 / N-RGO nanocomposite for hydrogen generation and electrochemical applications: New insights into the structure-performance relationship

Strenuous efforts have been dedicated to obtain efficient photocatalysts with an amplified hydrogen generation employing TiO2 and reduced graphene oxide (RGO). Accordingly, black - nitrogen doped TiO2/nitrogen doped reduced graphene oxide (BNTNG) has been strategically synthesized in low temperature/pressure, vacuum annealing process using ethanol for a better photocatalyst. The pyrrolic nitrogen stabilized photocatalyst (BNTNG-2 – 2h Ultrasonication) has found to show an augmented hydrogen generation and electrochemical potency than its 1 h and 3 h counterparts (BNTNG-1 and BNTNG-3) due to the attachment of C2H4 fragments from ethanol restoring sp2 hybridization in nitrogen doped reduced graphene oxide (NRGO). Meanwhile, reduction in hydrogen production and capacitance of BNTNGs than its white analogue can be substantiated to the presence of N-O species along with oxygen vacancies / Ti3+ in BNTNG promoting electron/hole recombination centers. The recyclability of the photocatalyst is ascertained over five consecutive cycles. Plausible mechanism has been proposed for the nuances of N-O moiety and restoration of sp2 graphitic structure in BNTNG-2.

Photo-fermentative hydrogen production by Rhodopseudomonas palustris CGA009 in the presence of inhibitory compounds

This study investigated Rhodopseudomonas palustris CGA009 biohydrogen production from compounds commonly found in lignocellulosic steam explosion hydrolysate, by examining the effect of individual inhibitory phenolic and furan compounds found in hydrolysates, under photo-fermentative anaerobic conditions. Since lignocellulose is often converted into ethanol via yeast-mediated fermentation, the tolerance of R. palustris CGA009 towards ethanol inhibition was also tested at a concentration range of 0.25–14% (v/v) under anaerobic photo-fermentative conditions. Hydrogen production was enhanced by compounds such as syringaldehyde (0.03 g/L), which accumulated total hydrogen of 960 mL over the cultivation period. In contrast, a reduction in hydrogen production of 1.4 fold was observed in vanillin-containing solutions (0.43 g/L), which obtained accumulated total hydrogen of 576 mL. Increasing ethanol concentrations reduced hydrogen production, but cell growth was not affected up to 1% (v/v), a fairly low concentration. R. palustris CGA009 can tolerate comparatively high concentrations of phenolic compounds, suggesting its use for lignocellulose hydrolysate detoxification and hydrogen production.

Risk-Informed Safety Analysis for Accident Tolerant Fuels

Accident tolerant fuels (ATFs) are being tested by different nuclear vendors and research organizations, and their introduction into the U.S light water reactor fleet is planned for the second half of the 2020s. Under the framework of the U.S. Department of Energy Light Water Reactor Sustainability (LWRS) Program, as part of the LWRS Risk-Informed Systems Analysis Pathway, research is being conducted at the Idaho National Laboratory (INL) to develop tools and methods that can help the industry to quantify the benefits from adopting ATF technology. In this paper we describe the developed risk-informed methodology including the safety analysis code improvements, and we present some results for selected accident scenarios. The developed methodology combines the INL state-of-the-art deterministic Best Estimate code RELAP5-3D and the probabilistic risk analysis tools RAVEN and SAPHIRE. The analyses are performed on a three-loop pressurized water reactor, simulating station blackout and large-break loss-of-coolant accidents and considering near-term ATFs or iron-chromium-aluminum and chromium-coated clads. Finally, we show how, applying our methodology, the new core damage frequency (CDF) can be assessed. The results indicate that the main benefit in introducing near-term ATFs is a significant reduction in hydrogen production during accident conditions. No significant CDF reduction was found.

Single and combined effects of amino polystyrene and perfluorooctane sulfonate on hydrogen-producing thermophilic bacteria and the interaction mechanisms

As a carrier of perfluorooctane sulfonate, nano-plastics are ubiquitous and finally enriched in the sludge, which is widely used as a raw material for the production of bioenergy (hydrogen or methane) by anaerobic digestion. However, there are still many unknowns about their metabolic toxicity to functional microbes (e.g. hydrogen-producing thermophilic bacteria). Therefore, single and combined effects of amino polystyrene (NPS: 70 nm; 0.2 mg/L) and perfluorooctane sulfonate (PFOS: 0.1, 1 and 5 mg/L) on hydrogen-producing thermophilic bacteria were investigated after exposure for 7 days at 55 °C and pH = 5.7. Single NPS exhibited obvious interference to the metabolism of thermophilic bacteria, resulting in a 53.9% reduction in hydrogen production. However, the combined NPS + PFOS produced an antagonistic effect, leading to a 31.6% reduction in hydrogen production. Nonetheless, the single and combined exposure did not alter the type of hydrogen production (acetic acid-type hydrogen fermentation). Moreover, single NPS and combined NPS + PFOS not only induced the changes of the composition of extracellular polymers (EPSs) and π bond structure of the protein in EPSs, but also decreased the activity of hydrolase in EPSs and surface charge of EPSs. Compared to single NPS exposure, NPS + PFOS-exposed thermophilic bacteria was less permeable to a semi-membrane permeable dye and produced less reactive oxygen species, but were still significantly higher than control group. In short, the main mechanisms of single NPS and combined NPS + PFOS were both to increase cell permeability and to induce oxidative stress. The addition of PFOS alleviated the toxic effect of NPS, but did not change its mechanism of toxicity.

Cell degeneration and performance decline of immobilized Clostridium acetobutylicum on bagasse during hydrogen and butanol production by repeated cycle fermentation

The cell degeneration and the fermentation performance decline during repeated cycle fermentation with immobilized Clostridium acetobutylicum on bagasse for hydrogen and butanol production was studied. The cell degeneration has been characterized in abnormality of a long-chain morphology through 7 cycles of repeated fermentation. The fermentation performance decline has been indicated by decrease of glucose consumption rate from 0.82 g/L/h to 0.22 g/L/h, reduction of hydrogen production and productivity from 6 L/L to 2.5 L/L and 170 mL/L/h to 40 mL/L/h, as well as the decrease of butanol production and butanol productivity from 6.5 g/L to 1.0 g/L and 0.18 g/L/h to 0.02 g/L/h, respectively. The ratio of hydrogen production and butanol production was in the range of 6–10 and 17–20 during the earlier three and later four cycles, respectively. The carbon flow directed to ethanol was higher during the later period of fermentation.

Extraction of electrons by magnetite and ferrihydrite from hydrogen-producing Clostridium bifermentans by strengthening the acetate production pathway

Conductive mineral nanoparticles, such as magnetite, can promote interspecies electron transfer between syntrophic partners. However, the effect of magnetite has only been inferred in intraspecific electron output. Herein, a hydrogen-producing strain, namely, Clostridium bifermentans , which holds several electron output pathways, was used to study the effect of magnetite on the intraspecific electron output manner. Additionally, insulated amorphous ferrihydrite, which was used as an extracellular electron acceptor, was selected to compare with magnetite. Electrons, which were originally used to generate hydrogen, were shunted with the addition of magnetite and ferrihydrite, which resulted in the reduction of hydrogen production and accumulation of Fe(II). Interestingly, more electrons (39.7% and 53.5%) were extracted by magnetite and ferrihydrite, respectively, which led to less production of butyrate and more acetate. More importantly, the increased electron extraction efficiency suggested that electroactive microorganisms can switch metabolic pathways to adapt to electron budget pressure in intraspecific systems. This work broadens the understanding of the interaction between iron oxides and fermentative hydrogen-producing microbes that hold the capacity of Fe(III) reduction.

Exergy analysis of a hydrogen and water production process by a solar-driven transcritical CO2 power cycle with Stirling engine

This study attempts to go beyond the conventional framework of the integrated solar transcritical CO2 power cycle works, aimed at further utilization of available exergy as much as possible. This paper proposed a novel system for hydrogen and fresh water production in which a Stirling engine used instead of a condenser, for the places with abundant access to solar radiation and sea, and least to freshwater sources. This proposal leads to further utilization of streams’ exergy through the system instead of wasting to the environment, and further power production by the engine followed by the higher products. The electrolyzer employed beside Reverse Osmosis (RO) desalination system, and takes full advantages of highly concentrated brine stream of desalination, eliminating the wastewater rejection through proposed system leading to attaining a near-ZLD approach in fresh water and hydrogen production. This reduces the adverse impacts of desalination’s wastewater on the environment. A thermodynamic and exergy analysis is carried out to compare the superiority of this study and investigate the effect of some key parameters on the overall performance of the system as well. The results showed that replacing the condenser by a Stirling engine reduces the exergy destruction through heat transfer from CO2 to an LNG unit. Exergy destruction was reduced from 16.7% to 8.8% for the above configuration for an ideal Stirling engine that exploits it to produce extra power which its minimum is at least 9 kW and 15 kW higher than CO2 and LNG power productions. Moreover, Entering RO brine stream, wasting 2.58 kW exergy, to the electrolyzer leads to NaClO and H2 production besides removing brine stream. In a power plant, sodium hypochlorite is used for disinfection of cooling systems and hydrogen can be used as a source of energy in fuel cells. An examination of some thermodynamic factors showed that higher CO2 turbine inlet pressure has an optimum value in producing fresh water and hydrogen, while the higher CO2 turbine inlet temperature slightly reduces the productions rate. The more recovery ratio also causes a sharp reduction in hydrogen production, whereas it has an optimum amount of fresh water production at recovery ratio equals to 0.47.

Thermodynamic analysis of hydrogen production via chemical looping steam methane reforming coupled with in situ CO2 capture

In this study, a detailed thermodynamic analysis of the sorption enhanced chemical looping reforming of methane (SE-CL-SMR), using CaO and NiO as CO2 sorbent and oxygen transfer material respectively, was conducted. The effect of different parameters, such as reactor temperature, pressure, H2O/CH4 ratio, CaO/CH4 ratio and CaO/NiO ratio was investigated. Moreover, the use of different sweep gases and oxidants for the re-oxidation/calcination cycle, like pure oxygen, air, steam and CO2, was specifically addressed. Conventional steam reforming (SMR) and sorption enhanced steam reforming (SE-SMR) were also investigated for comparison reasons.The results of thermodynamic analysis show that there are significant advantages of both sorption enhanced processes compared to conventional steam reforming. Presence of CaO sorbent in the reformer leads to higher methane conversion, hydrogen purity and yield at low temperatures (∼650°C). Addition of the oxygen carrier, in the chemical looping reforming concept, minimizes thermal requirements of the process, and results in superior performance compared to SE-SMR and SMR processes. A negative effect from NiO addition is reduction in hydrogen production (due to the reaction of part of methane with NiO to form CO/CO2). Hydrogen yield is up to 11% lower compared to SE-SMR for a NiO/CaO ratio of 0.7. It was found that only pure O2 can be used for re-oxidation/regeneration in order to reduce the energy requirements of the SE-CL-SMR process up to 26% compared to SE-SMR and up to 55% compared to conventional SMR.

Dynamics of hydrogen-producing bacteria in a repeated batch fermentation process using lake sediment as inoculum

In this study, we evaluated the effectiveness of lake sediment as inoculum for hydrogen production through dark fermentation in a repeated batch process. In addition, we investigated the effect of heat treatment, applied to enrich hydrogen-producing bacteria, on the bacterial composition and metabolism. Denaturing gradient gel electrophoresis and molecular cloning, both performed using the 16S rDNA gene as target gene, were used to monitor the structure of the bacterial community. Hydrogen production and bacterial metabolism were analysed via gas chromatography and high-performance liquid chromatography. Both treated and non-treated inocula were able to produce high amounts of hydrogen. However, statistical analysis showed a clear difference in their bacterial composition and metabolism. The heat treatment favoured the growth of different Clostridia sp., in particular of Clostridium bifermentans, allowing the production of a constant amount of hydrogen over prolonged time. These cultures showed both butyrate and ethanol fermentation types. Absence of heat treatment allowed species belonging to the genera Bacillus, Sporolactobacillus and Massilia to outgrow Clostridia sp. with a reduction in hydrogen production and a significant metabolic change. Our data indicate that lake sediment harbours bacteria that can efficiently produce hydrogen over prolonged fermentation time. Moreover, we could show that the heat treatment stabilizes the bacterial community composition and the hydrogen production.

Mechanism Reduction of Hydrogen Production from Dimethyl Ether Partial Oxidation by Plasma Reforming

Chemical reaction kinetic model of hydrogen production from DME partial oxidation by plasma reforming was found. Mole fractions of main products of DME partial oxidation by spark plasma as the function of inlet gas flow rate were calculated at atmospheric pressure and ambient temperature. Comparing the results of calculation and experiment, the model was proved to be correct. The mechanism research was done by the method of sensitivity analysis and rate of production. The reduced mechanism which includes 16 species and 13 radical reactions was done. The calculation results of reduced mechanism and detailed mechanism were close. The result shows that the reduced mechanism can be used in chemical reaction kinetic calculation of hydrogen production from DME partial oxidation by spark plasma reforming.

Hydrogen Source Diagram: A Procedure for Minimization of Hydrogen Demand in Petroleum Refineries

The consumption of hydrogen in petroleum refineries is increasing due to its growing intensive use in treatment processes and in new refining technologies. This trend and the reduction of hydrogen production in gasoline processing have generated a new panorama. In this new context, target identification for minimum consumption of hydrogen in a distribution network has become fundamental information in the definition of minimum hydrogen requirements in petroleum refineries. This paper presents the hydrogen source diagram (HSD), a new algorithmic method for minimum hydrogen consumption target calculation and, simultaneously, hydrogen network flowsheet synthesis. The proposed HSD procedure is described in details using a case study, showing its wide scope. The results demonstrate the effectiveness of the procedure and show that the generated network can be easily adapted to meet specific plant restrictions.

Effect of exogenous electron shuttles on growth and fermentative metabolism in Clostridium sp. BC1

In this study, the influence exogenous electron shuttles on the growth and glucose fermentative metabolism of Clostridium sp. BC1 was investigated. Bicarbonate addition to mineral salts (MS) medium accelerated growth and glucose fermentation which shifted acidogenesis (acetic- and butyric-acids) towards solventogenesis (ethanol and butanol). Addition of ferrihydrite, anthraquinone disulfonate, and nicotinamide adenine dinucleotide in bicarbonate to growing culture showed no significant influence on fermentative metabolism. In contrast, methyl viologen (MV) enhanced ethanol- and butanol-production by 28- and 12-fold, respectively with concomitant decrease in hydrogen, acetic- and butyric-acids compared to MS medium. The results show that MV addition affects hydrogenase activity with a significant reduction in hydrogen production and a shift in the direction of electron flow towards enhanced production of ethanol and butanol.

22 Orally administered xylose isomerase converts fructose to glucose – a promising approach in case of fructose malabsorption

Clinical proof: A preliminary observational study was performed with the capsules containing Xylose Isomerase. Volunteers with diagnosed symptomatic fructose malabsorption were advised to eat fructose-containing meals with or without the capsules and monitor the symptoms. 67% of the participants stated a „good effect“, 22% „little effect“ and 11% „no effect“ of the XI containing capsules in respect to intestinal irritation after consumption of fructose. A double-blind placebo-controlled clinical trial is currently in progress. The primary outcome of this study is the reduction of hydrogen production in the large intestine after ingestion of fructose with capsules containing verum or placebo.

Evaluation of the effect of rifaximin in colon diverticular disease by means of lactulose hydrogen breath test.

To understand better the mechanism by which rifaximin produces symptomatic relief in diverticular disease of the colon, the effect of this antibiotic on orocaecal transit time and on the production of hydrogen by intestinal microflora after ingestion of lactulose was studied in 33 patients with this disease and in 11 healthy subjects. An hydrogen breath test was carried out to measure pulmonary hydrogen excreted during the 3 hours after ingestion of 10 g lactulose. In patients, the hydrogen breath test with lactulose was repeated after treatment with 400 mg rifaximin twice daily for 10 days. In patients under basal conditions and controls, orocaecal transit time did not differ significantly, but hydrogen production was significantly higher in the former (p < 0.02). In patients, transit time and hydrogen excretion in response to lactulose administration did not differ significantly before and after treatment with rifaximin, and these two parameters were inversely correlated both before (r = 0.49, p < 0.01) and after rifaximin (r = 0.58, p < 0.001). Fifteen of the 33 patients showed accelerated transit time after treatment with the antibiotic, 10 showed no variation, and 8 showed prolonged transit. In 19 patients a reduction in hydrogen production was noted after rifaximin, while in 14 an increase was demonstrated. Twenty-one of the 33 patients reported an improvement in their symptoms with rifaximin; of these, only 10 showed accelerated transit time and 9 a reduction in hydrogen production after rifaximin.(ABSTRACT TRUNCATED AT 250 WORDS)